1. Field of the Invention
This invention relates to a constant-speed cruising control system for vehicles wherein the vehicle speed is automatically controlled to a desired crusing speed.
2. Description of the Prior Art
Heretofore, there has been a constant-speed cruising control system, for example, which is provided with a car-speed sensor for outputting car-speed data proportional to an actual vehicle speed, a command switch for outputting a command signal, a car-speed memory for storing the car-speed data from the car-speed sensor in response to an operation of the command switch, an actuator for driving a throttle in the opening or closing direction, and a control mechanism for giving a command signal to the actuator in accordance with difference between the actual vehicle speed and the stored vehicle speed.
In the constant-speed cruising control system, by operating a set switch of the command switch, the vehicle speed at the time of releasing the set switch subsequent to its pushing operation is stored in the car-speed memory, and the control mechanism gives a command to the actuator in accordance with the difference between the actual vehicle speed and the stored vehicle speed.
Therefore, the vehicle speed is maintained automatically at the constant cruising speed stored in the car-speed memory without operating an accelerator pedal by driving the throttle in the opening or closing direction so as to coincide the actual vehicle speed with the stored vehicle speed through the actuator.
In this state, if the brake pedal is depressed, the automatic control of the vehicle speed is cancelled so that the vehicle speed slows down.
After this, operating a resume switch of the command switch, the control mechanism returns the vehicle speed to the stored vehicle speed and controls the vehicle so as to cruise at the stored speed constantly by driving the throttle through the actuator in response to the operation of the resume switch (resuming control).
When the set switch or an acceleration switch of the command switch is operated (reset operation) during the resuming control the control mechanism newly stores vehicle speed at the time of operating the set switch or the acceleration switch and controls the vehicle speed constant at the speed newly stored at the time of the reset operation by driving the throttle in the closing direction so as to coincide the actual vehicle speed with the newly stored speed through the actuator in response to the reset operation of the set switch or the acceleration switch of the command switch.
However, the aforementioned conventional constant-speed speed cruising control system is so designed that control mechanism controls the throttle by outputting a deceleration signal to the actuator for the time equivalent to the amount of time the control mechanism outputs an acceleration signal to the actuator during a period of time from the operation of the resume switch till the reset operation of the set switch or the acceleration switch in order to switch over the vehicle from the acceleration state according to the resuming control to the state in which the vehicle speed is maintained at the speed newly stored in response to the reset operation. Therefore, there is the possibility that the throttle is driven in excess in the closing direction by the actuator at the time of switching over from the acceleration state to the cruising state at the constant-speed newly stored by the reset operation, and there is a problem since undershooting of the vehicle speed occurs and pleasant driving may be obstructed.